Hi,
Other than some technical details re ammo power, the main difference is that shooting in Std division, you are not allowed to have compensators or optical sights on your guns.
So, if by 'easier' you mean easier physically, I believe that a nicely tuned Open gun will give you less muzzle flip (but more noise, haha) than an equally well tuned Std gun. However, if you mean easier from a scores point of view, they are both equally tough.
Remember - division selection only specifies whose scores yours will be compared against - everyone shoots the same course of fire, the same level of match difficulty applies to everyone. With experience, you will become aware of small differences in divisions and how good shooters in each one might differ in their strategy/etc, but for now, it doesn't matter.
Ohhh, another thing - if by 'easy' you mean easy to get a gun that works, easy to get ammo for it, then you might want to look at joining us in the Production division - least expensive, most available ammo,and least expensive, most low-maintenance guns

I believe they are also the easiest to handle, physically, so if you have (for example) small hands, or weak arms, a Prod gun will probably be much less tiring to use than Open/Std.